Abstract: Based on the straw returning experiment in Hulan campus of Heilongjiang University, this study focused on the dynamic of soil urease activity at different nitrogen application rates after straw returning to the field, and tried to clarify the relationship between soil nitrogen content and urease activity under accelerated decomposition of corn straw in black soil. In the experiment, the soil total nitrogen, available nitrogen, and urease activities were measured in the main areas of straw decomposition and no straw application, with different nitrogen fertilizer levels (pure N) (0,135 kg/hm2,180 kg/hm2,225 kg/hm2) as sub-areas. The results showed that the changing trend of soil urease activity under the two straw treatments increased with the extension of maize growth period and decreased after reaching the maximum in the jointing stage. Compared with the treatment without straw, accelerated straw decomposition with nitrogen application rates of 180 kg/hm2 and 225 kg/hm2 could significantly improve soil urease activity (p< 0.05), while nitrogen application rates of 0 kg/hm2 and 135 kg/hm2 increased urease activity but no significant difference was detected(p>0.05). The changing trend of soil available nitrogen and soil total nitrogen is consistent with the change trend of soil urease activity, both of which increase with the increase of nitrogen application level. Significantly positive correlations between soil urease activity and total nitrogen or available nitrogen were observed in this study.